The present invention is related to light control elements and light control devices using a photonic crystal structure and applicable to light switches, optical intensity modulators, and the like.
A photonic crystal forms a photonic bandgap, which is a forbidden band of photons, as a result of dielectric periodical structure having a period corresponding to optical wavelength and exhibits singular effects due to its strong dispersion. Thus, photonic crystals are expected as an ultra minute optical integrated circuits or novel functional optical devices. By using these properties, it becomes possible to construct light control elements such as light switches or optical intensity modulators having an extremely minute optical path modification function.
Various structures are proposed for optical path switching devices according to the applications and according to the materials used therefor. For example, Japanese Laid-Open Patent Application 2002-221680 describes optical path switching by moving an optical path changing fluid with respect to an operation fluid having a matched refractive index, such that the optical path changing fluid has a refractive index different from the refractive index of the foregoing operation fluid.
Further, Japanese Laid-Open Patent Application 2002-122798 describes optical path switching achieved by moving a galvanometric mirror inserted between optical waveguides in the state that the mirror is sandwiched by electromagnets.
Further, in the field of optical telecommunication in trunk systems, a system using a reflector called MEMS (Micro Electro-mechanical system) is used.
In these conventional methods, there exists an advantage of achieving large extinction ratio with simple construction, while such a conventional construction has a drawback, associated with its construction of using mechanical movement of an object such as thermal pressure generator or electromagnet, that it is difficult to achieve high-speed switching.
As a high-speed optical switch, a device based on directional coupler formed of lithium niobate or a device of Mach Zehnder type is used generally, wherein such high-speed optical switches are already in commercial production. However, such conventional high-speed optical switches have a drawback in that the device length of several centimeters. Because of the large device length, it is difficult to use such an optical switch for the optical interconnection switch on a circuit board carrying a semiconductor chip thereon.
Meanwhile, there is a proposal of an optical path switch using a photonic crystal. Particularly, there is a proposal of an optical switch that uses the strong dispersion of a photonic crystal called super prism effect (Physical Review B, vol. 58, p. 10096, 1998).
For example, Japanese Laid-Open Patent Application 2002-303836 describes an optical path switch that uses super prism effect.
FIG. 18 shows an example of the construction proposed in the Japanese Laid-Open Patent Application 2002-303863.
Referring to FIG. 18, an optical beam incident to a photonic crystal 202 via an optical waveguide 201 obliquely with respect to an optical axis thereof travels in the direction of an arrow shown in continuous line due to the dispersion of the photonic crystal in the state no current injection is made. Thereby, the incident optical beam exits to an optical waveguide 203 of channel 1 (CH1).
When a current injection is made, on the other hand, the refractive index of the medium constituting the photonic crystal 202 is changed, and resultant change of the refractive angle results in a change of propagating direction in the photonic crystal as represented by the arrow shown in a broken line. Thereby, the incident optical beam is directed to an optical waveguide 204 of channel 2 (CH2). Thus, the optical path switch of FIG. 18 induces a large change of deflection angle in the incident optical beam by the super prism effect for switching the incident optical beam to the exit optical waveguide 204.
Meanwhile, there is a problem in such an optical switch element that uses a photonic crystal in that the super prism effect is extremely sensitive to the incident angle and wavelength of the incident optical beam and that there occurs a large change of deflection angle when there is caused a very small change of wavelength in-the incident optical beam. Further, there is a need of fixing the incident angle of the incident optical beam with respect to the photonic crystal. Further, there exist various problems to be solved such as existence of strong reflection at the edge surface of the photonic crystal.
Further, there is a concept of integrating a photonic crystal with an interferometer of Mach-Zehnder type or directional coupler for achieving optical modulation or optical path switching. However, there has been no known construction capable of achieving such objects. Further, there have been no known devices that are used in practice.